1. Field of the Invention
The present invention relates to a gas insulated circuit breaker and, in particular, relates to a gas insulated circuit breaker which employs an opening spring and a closing spring for circuit breaking and closing operations performed in its circuit breaking unit.
2. Description of Related Art
A gas insulated circuit breaker is, in general, composed of a circuit breaking unit including a pair of separable contacts disposed in a closed tank filled with SF.sub.6 gas, an actuating mechanism box which is ordinarily disposed outside the closed tank and which may accommodate an opening coil and a closing coil for providing an operation command to an actuating mechanism also accommodated therein, and a mechanism case which accommodates a link mechanism coupling between the actuating mechanism and a movable contact in the circuit breaking unit. For the actuating mechanism which is designed to cause circuit opening and closing operations in the circuit breaking unit, many types of actuating mechanisms, such as a pneumatic type actuating mechanism, a hydraulic type actuating machanism and a spring type actuating mechanism, are in use, and such actuating mechanisms are ordinarily accommodated in the actuating mechanism boxes.
JP-A-61-161628(1986), which corresponds to European Patent Publication No. 0186171, discloses a spring type actuating mechanism which uses an opening spring and a closing spring for circuit breaking and closing operations in the circuit breaking unit, wherein both the opening spring and the closing spring are disposed in an actuating mechanism box.
JP-A-63-304542(1988), which corresponds to U.S. Pat. No. 4,839,476, also discloses a spring type actuating mechanism, wherein both an opening spring and a closing spring are constituted by torsion bars and are disposed in an actuating mechanism box.
Further, JP-A-64-6340(1989) also discloses a spring type actuating mechanism which uses an opening spring and a closing spring for circuit breaking and closing operations in a circuit breaking unit, wherein the opening spring is disposed in an actuating mechanism box. However, the closing spring is disposed outside the actuating mechanism box.
With the gas insulated circuit breakers as disclosed such as in JP-A-61-161628(1986) and JP-A-63-304542(1988), however, wherein both the opening spring and the closing spring are disposed in the actuating mechanism box, a space occupying rate of the springs in the actuating mechanism box rises to thereby increase the size of the actuating mechanism box.
Further, with the gas insulated circuit breaker as disclosed in JP-A-64-6340(1989), for example, wherein only the opening spring is disposed in the actuating mechanism box, a load comparable to an actuating force of the opening spring acts on the secured end side of the opening spring as a reaction force, and a vibration caused thereby when the actuating force is exerted is directly transmitted onto the actuating mechanism box, and for these reasons there was a possibility that contacts such as in electromagnetic contactors and auxiliary contactors disposed in the actuating mechanism box are erroneously operated. Accordingly it was necessary to construct the actuating mechanism box to be sufficiently strong and large in order to avoid the above problems.